1. Field of the Invention
This invention relates to visual displays in general and more particularly to an improved infinity image display for use with vehicle simulators.
2. Description of the Prior Art
As the cost of training in actual vehicles, such as modern commercial and military aircraft, large ships, trucks, etc., has risen, there has been an increased demand for better simulators and trainers in which training can be done at a much lower cost. One way of improving simulation fidelity and the training value of such devices, is to include therein a display system which can provide the trainee with realistic visual cues. Ideally, such a visual display should provide an image that appears to be at infinity, over as large a field of view as is visible from the actual vehicle.
One of the best ways of developing an image at infinity is to use a spherical mirror as a collimator. In a well known simulator display system of this genre, a beamsplitter and spherical mirror are located in front of a trainee. The beamsplitter is used to fold the optical axis so that an input image source can be located out of the direct field of view of the trainee, at an elevated position optically equivalent to the focal surface of the spherical mirror. The input image is projected from said source down onto the beamsplitter, from which it is reflected forward onto the concave surface of the spherical mirror. The visual scene is then reflected back from the mirror, through the beamsplitter, to the trainee's eye, which is located on the optical axis of the display, near the center of curvature of the mirror.
Although any one of a number of available image generators can be employed with the above-described infinity image display, frequently a cathode ray tube (CRT), having its faceplate located in the focal plane of the spherical mirror, is used as the image source for the display. This CRT-mirror-beamsplitter combination is widely used in vehicle simulators, especially flight simulators, to provide realistic out-of-the-window scenes.
The primary deficiency of the CRT-mirror-beamsplitter display is that it provides only a limited vertical field of view. The CRT limits the top of the field of view and the intersection of the beamsplitter and the mirror, the bottom. The vertical field of view of the existing display is thus constrained to approximately 28.degree..
To enlarge the vertical field of view presented by such a CRT-mirror-beamsplitter display, the prior art has resorted to aerial images and tiered display systems. See, for example, U.S. Pat. Nos. 3,432,219; 3,709,581; and 3,659,920. The aerial image systems provide increased vertical field of view, but only with attendant increases in complexity, cost, size and light loss. The tiered systems suffer from similar disadvantages and are also plagued by alignment and maintenance problems.
In U.S. Pat. No. 3,785,715, it is suggested that the vertical field of view of a flight simulator infinity image display could be increased by moving the observer's eyepoint inside the center of curvature of the mirror. In practice, the interior configuration, of simulated cockpits makes such repositioning of the trainee impossible. This earlier patent also suggests that the display could be scaled larger than normal to displace rearwardly the center of curvature of the spherical mirror. This would, of course, result in an undesirable increase in display weight and size. Moreover, it should be noted that it is presently impossible to scale-up a display using a color CRT, since the largest available color CRT has only a 26" diagonal.
Thus there exists a need for a method and apparatus for increasing the vertical field of view from a standard mirror-beamsplitter infinity image display, without materially increasing the size, expense or complexity of the display, without requiring corrective lenses or tedious alignment procedures, and without deteriorating the quality of the final image provided by the display.